1. Field of the Invention
This invention relates to a process for the production of oligourethanes or urethane prepolymers containing terminal mercapto groups and to the use of these products in sealing compounds hardenable by oxidation or as an additive for crosslinkable epoxy resin systems.
2. Statement of Related Art
There are various known processes for the production of oligourethanes containing terminal mercapto groups using as starting material any of a variety of polyols which are reacted with excess diisocyanates or triisocyanates. According to the literature, suitable polyois also include the adducts of alkylene oxides, such as propylene oxide or ethylene oxide, and mixtures of the two alkylene oxides. Oligourethanes showing excellent processing properties are obtained when, starting from an adduct of propylene oxide and ethylene oxide with trimethylol propane, isophorone diisocyanate is first added so that a prepolymer still containing sufficient terminal isocyanaate groups is obtained. This prepolymer is then converted into an isocyanate-free oli-gourethane containing mercapto groups by reaction with at least the stoichiometrically necessary quantity of mercaptoethanol. Products obtained in this way are clear, substantially colorless and have a viscosity at room temperature of approximately 100 Pa.s.